diff --git a/Doc/using/cmdline.rst b/Doc/using/cmdline.rst
index b113c8f4489..a34666d2dc5 100644
--- a/Doc/using/cmdline.rst
+++ b/Doc/using/cmdline.rst
@@ -335,6 +335,8 @@ Miscellaneous options
 Environment variables
 ---------------------
 
+These environment variables influence Python's behavior.
+
 .. envvar:: PYTHONHOME
    
    Change the location of the standard Python libraries.  By default, the
@@ -350,7 +352,7 @@ Environment variables
 
 .. envvar:: PYTHONPATH
 
-   Augments the default search path for module files.  The format is the same as
+   Augment the default search path for module files.  The format is the same as
    the shell's :envvar:`PATH`: one or more directory pathnames separated by
    colons.  Non-existent directories are silently ignored.
    
@@ -400,6 +402,9 @@ Environment variables
    If this is set to a non-empty string it is equivalent to specifying the
    :option:`-i` option.
 
+   This variable can also be modified by Python code using :data:`os.environ`
+   to force inspect mode on program termination.
+
 
 .. envvar:: PYTHONUNBUFFERED
    
@@ -422,7 +427,40 @@ Environment variables
 
 .. envvar:: PYTHONDONTWRITEBYTECODE
 
-   If given, Python won't try to write ``.pyc`` or ``.pyo`` files on the
+   If this is set, Python won't try to write ``.pyc`` or ``.pyo`` files on the
    import of source modules.
 
    .. versionadded:: 2.6
+
+
+.. envvar:: PYTHONEXECUTABLE
+
+   If this environment variable is set, ``sys.argv[0]`` will be set to its
+   value instead of the value got through the C runtime.  Only works on
+   MacOS X.
+
+
+Debug-mode variables
+^^^^^^^^^^^^^^^^^^^^
+
+Setting these variables only has an effect in a debug build of Python, that is,
+if Python was configured with the :opt:`--with-pydebug` build option.
+
+.. envvar:: PYTHONTHREADDEBUG
+
+   If set, Python will print debug threading debug info.
+
+   .. versionchanged:: 2.6
+      Previously, this variable was called ``THREADDEBUG``.
+
+.. envvar:: PYTHONDUMPREFS
+
+   If set, Python will dump objects and reference counts still alive after
+   shutting down the interpreter.
+
+
+.. envvar:: PYTHONMALLOCSTATS
+
+   If set, Python will print memory allocation statistics every time a new
+   object arena is created, and on shutdown.
+
diff --git a/Misc/NEWS b/Misc/NEWS
index dbc0034c13a..e76e7333efc 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -12,6 +12,8 @@ What's New in Python 2.6 alpha 1?
 Core and builtins
 -----------------
 
+- Patch #1668: renamed THREADDEBUG envvar to PYTHONTHREADDEBUG.
+
 - Patch #602345: Add -B command line option, PYTHONDONTWRITEBYTECODE envvar
   and sys.dont_write_bytecode attribute. All these can be set to forbid Python
   to attempt to write compiled bytecode files.
diff --git a/Modules/main.c b/Modules/main.c
index 71c9c5909fb..3d4b9bed8c8 100644
--- a/Modules/main.c
+++ b/Modules/main.c
@@ -62,7 +62,7 @@ Options and arguments (and corresponding environment variables):\n\
 -B     : don't write .py[co] files on import; also PYTHONDONTWRITEBYTECODE=x\n\
 -c cmd : program passed in as string (terminates option list)\n\
 -d     : debug output from parser; also PYTHONDEBUG=x\n\
--E     : ignore environment variables (such as PYTHONPATH)\n\
+-E     : ignore PYTHON* environment variables (such as PYTHONPATH)\n\
 -h     : print this help message and exit (also --help)\n\
 -i     : inspect interactively after running script; forces a prompt even\n\
 ";
diff --git a/Python/import.c b/Python/import.c
index 8094f7d4779..d9550f5c682 100644
--- a/Python/import.c
+++ b/Python/import.c
@@ -1630,7 +1630,7 @@ case_ok(char *buf, Py_ssize_t len, Py_ssize_t namelen, char *name)
 	FILEFINDBUF3 ffbuf;
 	APIRET rc;
 
-	if (getenv("PYTHONCASEOK") != NULL)
+	if (Py_GETENV("PYTHONCASEOK") != NULL)
 		return 1;
 
 	rc = DosFindFirst(buf,
diff --git a/Python/thread.c b/Python/thread.c
index 3a2c7af6ff6..9a4dc251f9a 100644
--- a/Python/thread.c
+++ b/Python/thread.c
@@ -79,7 +79,7 @@ void
 PyThread_init_thread(void)
 {
 #ifdef Py_DEBUG
-	char *p = getenv("THREADDEBUG");
+	char *p = Py_GETENV("PYTHONTHREADDEBUG");
 
 	if (p) {
 		if (*p)